1. Field of the Invention
The invention relates to a projection-type display apparatus adapted to magnify and project an image generated From image forming means such as a CRT (Cathode-Ray Tube) onto a screen with the use of a projection lens system.
2. Description of Related Art
Conventionally, a color projection-type display apparatus having three, namely, red, green, and blue projection units 183x, 183y, and 183z as shown in a plan view of FIG. 1 has been well known. An optical axis 128k of the central projection unit 183y is at right angles to a screen 199 in the horizontal direction, while that of each side projection unit 183x, 183z is inclined a field angle .theta.1 to cross at the central portion of the screen 199. In order to focus the image all over the surface of the screen 199, in each of the side projection units 183x and 183z, a tube axis 121k of a projection tube 121 is inclined to the optical axis 128k of a projection lens 128 (by a tilt angle .theta.2 between the tube axis 121k and the optical axis 128k). In the case where the projection units 183 are inclined also in the vertical direction, the tube axis 121k of each projection tube 121 is vertically inclined to the optical axis 128k of the respective projection lens 128.
Meanwhile, for the application to a variety of models having different projection distances and screen sizes, the relative angle of the projection tube to the projection lens is necessary to be changed in a projecting-type display apparatus. Similary, in a projecting-type color display apparatus consisting of three projection units for red, green, and blue colors, the above relative angle should be set separately for each projection unit so as to meet the difference in the refractive indexes of the projection lenses.
As such, the projecting-type display apparatus has conventionally been so constructed as to be conformed to various kinds of projection units or different size of the screen that uses a common spacer block and separates a projection tube frame for holding a projection tube and a lens frame for holding a projection lens, thereby changing the relative angle between the frames.
FIG. 2 shows a diagrammatic transverse sectional view showing one projection unit of the projecting-type display apparatus disclosed in, for example, Japanese Utility Model Application Laid-Open No. 60-61881 (1985). A reference numeral 121 indicates a projection tube such as a CRT or the like, and 128 is a projection lens having a plurality of lens elements.
The projection lens 128 is held by a lens frame 153 having a through hole 128d in conformity with the outer peripheral shape of light at the entering side. A plurality of through holes 153v penetrating in the optical axis direction of a projection unit 183 are disposed at predetermined positions of the lens frame 153. Connecting bolts 104 each having a threaded portion 104a formed at the front end thereof are fitted with nuts 105 via washers 103 in the through holes 153v. The lens frame 153 is fixed by screws 163 to a fixing angle bar 170 to which the projection unit 183 is to be secured.
The projection tube 121 is fitted into a pressing plate 198 which is rigidly supported by screws 106 to a projection tube frame 151. In the projection tube frame 151, threaded holes 151m are opened at positions respectively opposite to the through holes 153v. The projection tube 121 is coupled to the projection lens 128 when the threaded portions 104a of the connecting bolts 104 are meshed into the threaded holes 151m of the projection tube frame 151. Since a plurality of connecting bolts 104 are rotated independently, the projection tube frame 151 can be inclined an arbitrary angle to the lens frame 153.
In the thus-configured projection unit 183, an image formed by the projection tube 121 is magnified and projected by the projection lens 128 to obtain a large screen. As shown in FIG. 1, generally, three sets of projection units 183 for red, green, and blue colors and each consisting of the projection tube 121 and the projection lens 128 are provided, so that images from the three projection units 182x, 183y, and 183z overlap with each other to form a color image on the screen 199.
As described above, in each projection unit 182x, 183y, and 183z, the tilt angles must be adjusted and the adjustment is realized by rotating the connecting bolts 104 thereby to incline the projection tube frame 151. This allows the tube axis 121k of the projection tube 121 to shift in an arbitrary direction from the optical axis 128k of the protection lens 128. Consequently, the distance S between a lens face 128b of the projection lens 128 and a display face 121c of the projection tube 121 can be adjusted in the vertical and lateral directions of the screen 199, whereby the image is projected in optimum focus to the screen 199.
In the above-mentioned arrangement, however, the rotating center of connecting bolts 104 incline the projection tube with respect to the projection lens may not be constant, or the distance between the projection lens and the projection tube may be changed, thus obstructing the focusing function. Since the air is present between the projection lens and the projection tube, moreover, the arrangement has a drawback that the light emitted from the projection tube is irregularly reflected before entering the projection lens, deteriorating the contrast.
As another prior art example, FIG. 3 shows a section view of a projection unit of a projecting-type display apparatus disclosed in Japanese Patent Application Laid-Open No. 5-40309 (1993). A projection tube 121 is attached to a projection tube frame 151 in the watertight state. An outer peripheral wall 151g of the projection tube frame 151 is formed into a spherical surface, and fitted into a holding portion 161 having a curved guide 161a in such a manner that the projection tube frame 151 is rotatable to the holding portion 161. On the other hand, a projection lens 128 is attached to a lens frame 153 in the watertight state. An outer peripheral wall 153g of the lens frame 153 is a spherical surface, and fitted into the curved-face guide 161a of the holding portion 161. The lens frame 153 is rotatably mounted to the holding portion 161.
A reference numeral 155 indicates a bellows functioning as a coupler which connects the projection tube frame 151 with the lens frame 153 in the watertight state. A cooling liquid 132 is filled in an inside space 131 of the bellows. The inclining angle of the projection tube frame 151 to the lens frame 153 is adjusted by an adjusting screw 164 which passes through the projection tube frame 151 and is meshed with the lens frame 153.
In the thus-constructed projection unit 183, as a display face 121c of the projection tube 121 is heated to considerably high temperatures when an image is projected, the heat is transmitted via the cooling liquid 132 to the lens frame 153 and the projection tube frame 151 made of aluminum having excellent heat-conduction properties, to be radiated from the frames.
For the cooling liquid 132, for instance, ethylene glycol, silicone, or the like is used. Since these kinds of material have a refractive index of the same level as that of glass forming the projection tube 121 and the projection lens 128, the cooling liquid 132 is also effective to prevent the light from the projection tube 121 from being irregularly reflected, in addition to dissipate the heat. Therefore, the deterioration of the contrast of an image projected by the projection lens 128 is prevented, with high luminance achieved.
In the projection unit of the aforementioned type, the tilt angle .theta.2 of each project,on unit 182x, 183y, 183z in the horizontal direction, and in the vertical direction is changed by rotating the adjusting screw 164, and the focus is properly met both at the center and periphery portions of the screen.
However, the prior art apparatus has a disadvantage in that an inclination reference point used to adjust the tilt angle is an imaginary point and therefore an inclination point cannot be verified. Since the inclination guide slides on a face, the frictional resistance is large. Moreover, when the optical axis is adjusted by using a spherical guide, the guide should be processed with high accuracy so as to fit the concave and convex faces, which increases processing costs. Furthermore, since the apparatus cannot be assembled without dividing the holding portion thereoutside, not only processing accuracy, but assemblying accuracy is required.
FIG. 4 is a section view showing the main portion of a projection unit of a prior art projecting-type display apparatus revealed in Japanese Utility Model Application Laid-Open No. 2-41979 (1990), and FIG. 5 is an exploded perspective view of the projection unit. A reference numeral 201 indicates a projection tube, and 202 designates a spacer block made of a material such as diecast aluminum of superior heat-conduction properties. A wall portion 202a, and a boss portion 202c having threaded holes 202b are formed at, one side of the spacer block 202 to which the projection tube 201 is attached. A pressing plate 203 is fitted to the projection tube 201. The pressing plate 203 has a contact hole 203a butting against an outer peripheral wall 201a of the projection tube 201, and mounting holes 203b respectively located at four corners of the plate 203. The mounting holes 203b of the pressing plate 203 correspond to the boss portion 202c of the spacer block 202. A post 204 with a spring 205 in the outer periphery is inserted in each of the mounting holes 203b into touch with the boss portion 202c. A screw 207 passing through a washer 206 runs is passed through the post 204 and is fitted into the corresponding threaded hole 202b of the boss portion 202c. In consequence, the projection tube 201 is pressed to the spacer block 202 while being uniformly pressed thereto by the pressing force of the springs 205. A deflection yoke 208, a focus magnet 208, and a CRT board 210 are attached to the projection tube 201.
On the other hand, a barrel 211a of the projection lens 211 is attached to the other side of the spacer block 202 by screws 212. A projection tube packing 213 is disposed between a display face 201b of the projection tube 201 and a projection tube mounting face 202d of the spacer block 202, and a lens packing 214 is set between a lens face 211b of the projection lens 211 and a lens mounting face 202e of the spacer block 202. A space 215 defined by the projection tube 201, the projection lens 211, and the spacer block 202 is kept to be in the watertight state and filled with a cooling liquid 216 such as ethylene glycol and so on. An expansion content produced when the cooling liquid 216 thermally expands is accommodated in a tank 217. The cooling liquid 216 blocks the light emitted inside the display face 201b of the projection tube 201 not to return to the fluorescent screen, thereby preventing the contrast of a projection image from being degraded. The heat which, when the projecting-type display apparatus operates, is generated at the display face 201b of the projection tube 201 is transmitted via the cooling liquid 216 to the spacer block 202, to be discharged outside.
The prior art apparatus in FIG. 4 is constituted of three projection unit, and therefore requires three kinds of spacer blocks 202. In applying the apparatus to different projection distances and screen sizes, it is required to manufacture spacer blocks 202 of different sizes, increasing the design time or costs of die casting molds.
The mounting posture of the projection tube 201 with respect to the projection lens 211 depends on the processing accuracy of the spacer block 202. Even if the apparatus is enormously assembled, no correcting means is provided in the prior art.
FIG. 6 is a section view showing the main portion of a projection unit of a projecting-type display apparatus discussed in Japanese Patent Application Laid-Open No. 43-52141 (1992), and FIG. 7 is a partial enlarged view of the projection unit. In the figures, a projection tube 201 is mounted in the watertight state to one side of a projection tube frame 218 via a first O-ring 219 installed in an annular groove 218a formed in the periphery of an opening of the projection tube frame 218. On the other hand, a projection lens 211 is attached in the watertight state at one side of a lens frame 220 via a second O-ring 221 in an annular groove 220a formed at the peripheral edge of an opening of the lens frame 220.
Between the projection tube frame 218 and the lens frame 220, a cylindrical bellows 222 made of a metallic material containing iron such as stainless steel and urged in the axial direction is attached in the following manner: Rings 223 and 224 which have a plurality of mounting holes 223a and 224a separated a distance in the circumferential direction and function as mounting flanges are welded to both ends of the bellows 222. The ring 223 is held in the watertight state at the other side of the projection tube frame 218 via a third O-ring 225 which is disposed in an annular groove 218b formed at the peripheral edge of the opening of the projection tube frame 218, by tightening the mounting holes 223a of the ring 223 by screws 226. Similarly, the ring 224 is supported in the watertight state at the other side of the lens frame 220 via a fourth O-ring 227 set in an annular groove 220b at the peripheral edge of the opening of the lens frame 220, when the mounting holes 224a of the ring 224 are screwed by screws 228. A cooling liquid 216 is filled in the space in the watertight state. According to the above arrangement, the heat of a display face 201b of the projection tube 201 heated to very high temperatures is transmitted via the cooling liquid 216 to the spacer frame 202 made of diecast aluminum showing excellent heat conduction properties, and dissipated from the spacer.
The lens frame 220 is slidably supported by a holding portion 229 having a spherical face in touch with the frame. The projection tube 218 is coupled to the holding portion 229 by an adjusting mechanism 232, so that the relative angle of the projection tube 218 to the holding portion 229 is variable.
FIG. 8 is a diagram showing the projecting-type display apparatus having three projection units 234 configured as described above with reference to FIGS. 6 and 7. In the same manner as in the apparatus shown in FIG. 1, the center projection unit 234 is disposed at right angles to a screen 235, and the side projection units 234 are inclined to the screen 235 by the field angle .theta.1. In each side projection unit 234, a projection tube block 230 comprising the projection tube 201 attached to the projection tube frame 218 via the first O-ring 219 is disposed with the tilt angle .theta.2 to a lens block 231 in which the projection lens 211 is fitted to the lens frame 220 via the second O-ring 221. The tilt angle .theta.2 is adjusted by the adjusting mechanism 232. Accordingly, images from the three projection units 234 overlap with each other on the screen 235, and the focus is not even at the periphery portion of the screen.
In the prior art apparatus, although the relative position between the projection tube 201 and the projection lens 211 is adjusted by the adjusting mechanism 232, it is important to maintain the space 215 in the watertight state during the time so as to prevent the cooling liquid 216 from leaking. However, the cooling liquid 216 is sealed at four points in the apparatus and, four sealing members are requited. In other words, there are four potentially dangerous points to leak the cooling liquid 216, making the apparatus inferior in terms of costs and reliability.
When the bellows 222 is to be fixed by the screws, either the projection tube frame 218 or the lens frame 220 obstructs the fixing work, lowering the efficiency. Since the bellows 222 is made of a metal, the bellows lacks flexibility, and the volume of the bellows cannot be changed even when the cooling liquid 216 expands by the heat of the projection tube 201. Further, the distance between the projection tube frame 218 and the lens frame 220 should be secured long to mount the bellows 222.
FIG. 9 is an exploded perspective view showing a projection unit of a prior art projecting-type display apparatus, and FIG. 10 is a side section view of the projection unit. A projection tube 1 such as a CRT or the like as image forming means is held by a substantially box-like unit base 6 having a rectangular front opening into which the projection tube 1 is to be fitted. A face portion 1a of the projection display apparatus is fixedly bonded to a CRT cover 40 having a recessed portion slightly smaller than the face portion la, and a flange 40a surrounding the recessed portion. More specifically, the face portion 1a is fixed in the fluid-tight state to the recessed side of the CRT cover. A cooling liquid 9 is filled in a space 7 defined by the face portion 1a and the recessed portion.
In the figures, a projection lens 2 magnifies and projects an image formed by the projection tube 1. The projection lens 2 is screwed to a lens bracket 41. The lens bracket 41 and the CRT cover 40 are fixed to the unit base 6 by sending four stud bolts 42 erected in the vicinity of four corners of the opening of the unit base 6 through holes formed at the four corners of each of the lens bracket 41 and the CRT cover 40, and then fastening the bolts with nuts 43. Spacers 44 and 45 in a wedge-shaped section of a different thickness are held between the CRT cover 40 and the unit base 6 in a manner to decrease the thickness to the inner side.
One projection unit is thus comprised of the projection tube 1 and the projection lens 2 assembled as above. In general, a projecting-type color display apparatus includes, three, i.e., red, green, and blue projection units attached to the unit base 6. In FIGS. 9 and 10, only one projection unit for red color is illustrated.
FIG. 11 is a diagram showing the main portion of a projecting-type display apparatus having three sets of projection units. The red, green, and blue projection units R, G, and B are arranged in this sequence in such a manner that the optical axes thereof cross each other at the center of a screen 99. The light emitted from the green projection unit G which is disposed at the center of the units enters the surface of the screen 99 at right angles. The light from the red projection unit R set at the left side in a plan view, and that projected from the blue projection unit B at the right side enter the surface of the screen 99 at a required field angle .theta.1. In order to bring the peripheral portion of an image into focus, the projection tube 1 is so arranged as to assume the tilt angle .theta.2 to the optical axis of the projection lens 2. For attaining the required field angle .theta.1, each of the red and blue projection units R and B uses a pair of spacers 44 and 45 of a different thickness as shown in FIGS. 9 and 10, while the green projection unit G employs a pair of spacers having the same thickness.
In the thus-configured projecting-type display apparatus, images formed by the projection tubes 1.sub.R, 1.sub.G, and 1.sub.B are magnified and projected by the respective projection lenses 2.sub.R, 2.sub.G, and 2.sub.B thereby to form an image on the screen 99.
Generally, the field angle .theta.1 and the tilt angle .theta.2 are adjusted at the manufacturing stage of the apparatus in the configuration shown in FIG. 11, that is, the apparatuses are manufactured separately for each screen size and each projection distance. In such prior art projecting-type display apparatuses as above, the field angle .theta.1 is changed by replacing the spacers with spacers of another combination of thickness after loosening the bolts 43.
When the field angle .theta.1 is to be changed in the aforementioned method, it is necessary to prepare spacers of different combinations of thickness, and therefore the number of parts is increased. In the case where the projecting-type display apparatus is to be finely adjusted at the installing site of the apparatus, the worker is obliged to carry spacers of various kinds of thickness. Although the field angle .theta.1 is required to be changed minutely, because of the small difference in thickness of the spacers, it, is difficult for the worker to detect the screen size and the projection distance of the subject projecting-type display apparatus.
The projection lens 2 and the projection tube 1 are fastened by the common nuts 43. When the nuts 43 are loosened to replace the spacers 44 and 45, the projection lens 2 and the projection tube 1 become unstable, leading to unexpected accidents.
Since the three projection units are placed in proximity to each other, moreover, it is hard to replace the spacer between two projection units due to the narrow space and the efficiency is lowered.